Adult-type rhabdomyosarcoma

Rhabdomyosarcomas more commonly afflict children and adolescents.  It is rare in adults, accounting for 1% of all soft tissue sarcomas.  In adults, rhabdomyosarcomas are embryonal (34%), alveolar (23%) or pleomorphic (43%), rarely spindle cell or sclerosing.  Adult-type excludes embryonal and alveolar types. Most so-called rhabdomyosarcomas in adults within the internal trunk are in fact dedifferentiated liposarcomas with heterologous rhabdomyoblastic differentiation, as evidenced by MDM2 and CDK4 amplification.  

Epidemiology

Clinical features

True adult rhabdomyosarcomas occur predominantly in the lower limb, trunk wall or upper limb.

Radiology

Macroscopic appearances

Tumours most often arise in deep soft tissues, often striated muscle.  They are typically circumscribed and lobulated.

Histopathology

Three morphological types have been described, based on the predominant cellular pattern:

• Spindle cell: there are long intersecting fascicles of atypical spindle cells.  The cells have elongated nuclei and scant cytoplasm.  There may be foci of sclerosis.
• Pleomorphic:  more than 80% of cells are large and polygonal, often multinucleate.  Some cases show a background of smaller cells with scant cytoplasm.
• mixed: approximately equal spindle cella and pleomorphic components.

The mitotic rates are very variable, as is the extent of necrosis. Cross striations are not seen.

Immunohistochemistry

Positivity for desmin and myogenin is a sine qua non.  

Ultrastructure

Differential diagnosis

• Alveolar rhabdomyosarcoma:  positive for PAX3 or PAX7 / forkhead homolog 1 translocation.
• Malignant peripheral nerve sheath tumour with heterologous rhabdomyoblastic differentiation (malignant Triton tumour): often arises in type I neurofibromatosis, tumours often arise from a  nerve trunk; rhabdomyoblastic differentiation is focal.
• Dedifferentiated liposarcoma with heterologous rhabdomyoblastic differentiation: often retroperitoneal: show MDM2/CDK4 amplification by immunohistochemistry, FISH or PCR
• Spindle cell rhabdomyosarcoma vs. leiomyosarcoma: both may be positive for SMA: rhabdomyosarcoma should be positive for myogenin but negative for h-caldesmon.

Management

Surgery when possible, with adjuvant radiotherapy or chemotherapy.

Prognosis

The five year survival is approximately 50%.  Spindle cell rhabdomyosarcoma is aggressive compared with the childhood counterpart.  Sclerosing rhabdomyosarcoma also has a poor prognosis.

References

1 Stock N, Chibon F, Binh MB, Terrier P, Michels JJ, Valo I, et al. Adult-type rhabdomyosarcoma: analysis of 57 cases with clinicopathologic description, identification of 3 morphologic patterns and prognosis. Am J Surg Pathol. 2009 Dec;33(12):1850-9.

2 Furlong MA, Mentzel T, Fanburg-Smith JC. Pleomorphic rhabdomyosarcoma in adults: a clinicopathologic study of 38 cases with emphasis on morphologic variants and recent skeletal muscle-specific markers. Mod Pathol. 2001 Jun;14(6):595-603.

3 Gaffney EF, Dervan PA, Fletcher CD. Pleomorphic rhabdomyosarcoma in adulthood. Analysis of 11 cases with definition of diagnostic criteria. Am J Surg Pathol. 1993 Jun;17(6):601-9.

This page last revised 29.3.2010

©SMUHT/PW Bishop